BITU'MEN (Lat., a kind of mineral pitch). A name applied to a number of inflammable mineral substances varying in chemical composition and ranging in consistency from solid to gaseous. The bitumens consist mainly of carbon and hydrogen, but usually they contain also small amounts of sulphur, oxygen, and nitrogen. The most important substances included under the name are natural gas, naphtha, petroleum, maltha, mineral tar, asphalt, elaterite, wurtzilite, albertite, grahamite, gilsonite, ozocerite, and coal. Natural gas is composed mostly of marsh-gas, with small quantities of other hydrocarbons and of carbon oxide. Petroleum and naphtha and the solid bitumens are essentially hydrocarbon compounds, containing also subordinate amounts of sulphur, oxygen, and nitrogen, and other elements which may be regarded as impurities. The bitumens are widely distributed over the earth's surface, and occur in all the geological formations from the Silurian to the present. Their origin in most eases can be traced to the decomposition of vegetable matter, but various theories have been advanced to account for the deposits of petroleum. The several bitumens are desicribed in special articles. See Anthracite; Asphaltic Coal; Bituminous Coal; Lignite; Coal; Gas (Natural); Naphtha; Petroleum; Asphalt; Bituminous Limestone; Bituminous Shale; Elaterite; Albertite; and Grahamite.